Linda Lee, president of the Greater San Diego Association of Realtors, is the author of this guest post. U-T San Diego will periodically feature real estate advice columns from the association in this blog.

Shopping for a house can be exciting, but there is one factor above all others that deserves early consideration.

Be careful about where you set your sights. I have worked in real estate during all kinds of market conditions, and one of the biggest recurring mistakes I see is people who buy more home than they can afford.

Too many people end up suffering through the frustration and humiliation of losing their dream home because, in the end, they simply couldn’t afford it. For most buyers, the rule of thumb is to set your price range at around four to five times your gross income.

With interest rates at historic lows, you may have a window of opportunity to obtain your dream home. Monthly payments are lower on any given loan than they have been in years, and most rates are fixed for 15 years or 30 years so you can predict your housing costs into the future.

Pre-approval for a mortgage, not pre-qualification, is an absolute must. Prequalification is simply a lender’s estimate of how much you could be eligible to borrow and does not mean you will get a loan. Pre-approval means providing your lender with a fully completed loan application and all supporting documents proving your income, assets, credit and liabilities before you start house hunting. With this done, you can be confident about the price range you are considering and more importantly ready to act when you find that perfect home.

Next, do anything you can to come up with a 20 percent down payment. This can greatly reduce the interest rate you will have to pay on your loan and eliminates the need for costly mortgage insurance on top of your monthly mortgage payment.

Stay in your price range and your prudent judgment may put you in a larger and more expensive home sooner than you think.